A disk drive, commonly referred to as a direct access storage device, has one or more disks for storing data in the form of discrete magnetic transitions. The disks are somewhat analogous to compact disks which are used in a CD player in that they are both round, and hold a large amount of digital data. In a disk drive, however, multiple disks are mounted to a spindle, and spaced apart so that they do not touch each other. Currently, disks range from 48 millimeters (1.8 inches) to 130 millimeters (5.25 inches) in diameter.
The surface of each disk is smooth and uniform in appearance. Data on the disks in a disk drive is not stored in grooves, but in tracks. Each disk surface has a number of data tracks situated in concentric circles. The tracks on the disk essentially replace the grooves in a 45 rpm record. Each track in a disk drive is further subdivided into a number of sectors which is just one portion of the circumferential track.
Disks in a disk drive are made of a variety of materials. The substrate has been made of glass, plastic or metal. In the case of magnetic recording, a magnetizable layer of metal is placed on the substrate. Data is stored on such a disk by magnetizing small portions of the magnetizable layer of the disk. The portions magnetized will be in one or more of the sectors mentioned above. The data is usually transformed or encoded into a more compact form before it is recorded on the disk. Each portion so magnetized can be thought of as representing either a one or zero.
In order to magnetize the surface of a disk, a small ceramic block, called a slider, containing an electromagnetic transducer, known as a read/write head is passed over the surface of the disk, following the tracks. More specifically, the read/write head is flown at a height of approximately 0.15 micrometers (six millionths of an inch) or less from the surface of the disk. During flight, over the disk surface, the read/write head is energized to various states, causing a domain within a sector in the track below it to be magnetized.
To retrieve data stored on a disk, the read/write head is flown over the disk again. This time, the small magnetized domains of the disk induce a current in the read/write head transducer. By detecting the current from the read/write head, and decoding multiple occurrences from many domains, the data is reconstructed and then used by the computer system.
Like a record, both sides of a disk are generally used to store data or other information necessary for the operation of the disk drive. Since the disks are held in a stack and are spaced apart from one another, both the top and the bottom surface of each disk in the stack of disks has its own read/write head. Sometimes, a disk surface is dedicated to containing servo information. Servo information is made up of magnetized portions of the disk that contain information about the position of the head on the disk. Such servo information from one disk can help in determining where the heads on all the other disks are located. Further help may be provided by including some servo information in each sector on the disks.
The ceramic material comprising the slider, and the head which the slider supports are moved over the surface of the disk using an actuator arm. The actuator arms for multiple heads look like a comb, each tooth of the comb extending between the disks, and holding a head adjacent a disk surface by means of a suspension. A motor coupled to the comb that is referred to as an E block rotates the E block about its spine, causing the heads to move in a direction radial to the disks. The motor is controlled based on feedback from the servo information and with knowledge of where the desired data is physically located on the disk.
The slider is aerodynamically designed to fly close to the disk surface. Some sliders are subjected to a physical force or bias toward the disk surface by the suspension while others may be reverse biased, so that they actually tend to move away from the disk surface. When the disk starts to rotate, the aerodynamic effect causes the slider to fly. Fluid next to the disk, be it air, or a lubricant, provides a cushion, which causes some sliders to be lifted up, from the surface of the disk when the disk reaches a desired rotational velocity. In the case of a reverse biased slider, the pressure becomes less between the disk and the slider, causing the slider to move closer to the disk. In either case, the fly height of the slider is very small as previously stated.
The very close fly height can lead to problems when one considers the size of contamination inside the disk drive device. Most disk drives are sealed, and have filters which try to take particles away from the disk surfaces. Such disk drives are usually assembled in a clean room, to help ensure that particle contamination is minimized. In spite of such precautions, particles are still generated in the form of human skin flakes and plastic and steel particles having masses on the order of nanograms and picograms. Such is the magnitude of the contamination problems that are currently being faced. In spite of all the precautions, some particles may get caught in a lubricant that is used to keep the sliders from causing wear on the disks when the disk drive has been powered down. Such particles can easily smear on the disk surface, and sometimes actually destroy data stored on the disk or damage data heads. Collisions between heads and particles have become known as "head crashes" because of the damage that occurs. Dust particles can be disastrous. Other particles also can cause damage, even though they are much smaller than common dust.
U.S. Pat. No. 4,594,617 issued to Tezuka, describes problems related to dust or debris that accumulates on the head while the magnetic medium is rotating in a fixed direction. The solution was to use a cleaning medium, and rotate it at a slow rate, in the opposite direction. This is stated to work for cleaning the head, but does not address the problem of cleaning the disk itself. It also requires access to the disks, which is not practical in a sealed disk drive device.
In U.S. Pat. No. 4,263,634 to Chennoweth, a floppy diskette jacket which houses a data disk was provided with a wiping material. The material was set back from the opening in the housing so that fibers from the material did not interfere with the heads that were reading data from the disks in the opening. Again, the contamination problems faced here were related to dust sized particles. The disk surfaces were exposed to normal atmosphere. The size of the particles which cause problems in today's sealed disk drive devices are orders of magnitude smaller than those faced by Chennoweth.
In U.S. Pat. No. 3,609,721 issued to Meneley, dust particles were cleared from a disk surface by rotating the disk at normal operating speed while a read/write head having a slider with a round spherical bearing face was slowly swept across the surface of the disk. It was believed by the inventor that some particles struck the rounded side of the slider, and were dislodged. There was also described, a strong movement of air laterally outward from under the slider, which helps to carry dislodged particles, and other particles not so dislodged, clear of the slider. The slider was moved radially outward from the disk center by about one fourth the width of the slider per rotation of the disk.
Fibers contacting the disk surface were used in U.S. Pat. No. 3,366,390 issued to Applequist et al. to dislodge dust particles. Air flow from the rotating disks then carries the particles off of the disks.
All of the previous solutions were directed toward larger particles than presently are encountered. Such large particles were easily dislodged, and spun off the disk surface. The small particles which cause problems in today's disk drive devices do not dislodge so easily. The prior solutions have not proven effective in clearing disk surfaces of such debris.